Editorial highlights

Abstract

Every organism is a model organism for understanding development, evolution, disease, and regeneration, and we have only begun to scratch the surface of the interdisciplinary genetic, molecular, cellular, and developmental mechanisms that regulate these biological processes. These “Highlights” denote exciting advances recently reported in Developmental Dynamics that illustrate the complex dynamics of developmental biology.

“Review on pathogenesis and treatment of Alzheimer's disease” by Jinxia Cai, Yanqing Liu, and Haojun Fan. DevDyn 254.4, pp. 296–309. https://doi.org/10.1002/dvdy.762

Alzheimer's disease is a progressive neurodegenerative disorder, characterized primarily by memory and visuospatial skills impairment, personality or behavioral changes, and executive dysfunction. Alzheimer's disease, which has been speculated to begin in an individual up to 20 years before the onset of any symptoms, is increasing in prevalence and incidence. Age, genetics, environment, lifestyle habits, emotions, education, disease, and race are all considered to be causative factors in the etiology and pathogenesis of Alzheimer's disease, but despite extensive research and our improved understanding of β-amyloid aggregation, hyperphosphorylated tau, and neuroinflammation in its pathogenesis, there are currently no effective treatments to ameliorate or prevent neurodegeneration. This review article provides a timely and comprehensive analysis of the underlying etiology and pathogenesis of Alzheimer's disease, as well as an overview of potential Alzheimer's disease treatments.

“ARHGAP29 promotes keratinocyte proliferation and migration in vitro and is dispensable for in vivo wound healing” by Lindsey Rhea, Tanner Reeb, Emily Adelizzi, Bailey Garnica, Allison Stein, Alexis Kollash, Elliot Dunnwald, and Martine Dunnwald. DevDyn 254.4, pp. 310–329. https://doi.org/10.1002/dvdy.759

Skin, which is the body's largest organ, performs many functions. It helps to regulate temperature, prevent water loss, enable tactile sensation, and serve as a protective structural barrier to external environments. Composed of epidermis, dermis, and hypodermis, perturbations of skin development and homeostasis are associated with disease and defective wound healing. Proper maintenance of epithelial integrity requires the coordinated proliferation and migration of keratinocytes, which can rapidly respond to changes in the extracellular environment. The Rho family of GTPases, including Rac, Cdc42, and Rho, is a key regulator of cell morphology, migration, and wound healing. The authors previously showed that interferon regulatory factor 6 (IRF6) promotes keratinocyte migration via RhoA and is required for proper wound healing, especially in the surgical repair of orofacial clefts. In this study, the authors propose that ARHGAP29, which is a RhoGTPase that preferentially regulates RhoA, is a downstream effector of IRF6 and plays an important role in keratinocyte biology and wound healing.

“Seasonal heterochrony of reproductive development and gene expression in a polymorphic salamander” by Madison Herrboldt, Claire Wright, and Ronald Bonett. DevDyn 254.4, pp. 330–347. https://doi.org/10.1002/dvdy.744

Life cycle evolution can include ecological transitions and shifts in the timing of somatic and reproductive development. But when such heterochronic shifts are tissue specific, this can lead to the diversification of traits and morphological or behavioral adaptation. Salamanders exhibit alternative life cycle polymorphisms involving either an aquatic to terrestrial metamorphosis (biphasic) or retention of aquatic larval traits into adulthood (paedomorphic). In this study, the authors histologically and molecularly evaluate how life cycle evolution impacts temporal reproductive patterns in males of a polymorphic salamander. The authors discovered that changes in the distribution of androgen signaling in the integument (skin) correlated with differences in seasonal reproductive gland development and pheromone gene expression, which provides a potential mechanism for the differential diversification of reproductive traits.

“Patterns of early embryogenesis and growth in the olfactory system of chick (Gallus gallus domesticus) based on iodine-enhanced micro-computed tomography” by Aneila Hogan, Donald Cerio, and Gabriel Bever. DevDyn 254.4, pp. 348–364. https://doi.org/10.1002/dvdy.746

The vertebrate olfactory system governs our sense of smell through the detection of odorants by specialized neurons in the olfactory epithelium, which then transmit signals to the olfactory bulb and cortex for processing. It begins with the formation of the nasal placodes, paired bilateral thickenings of surface ectoderm, which give rise to the olfactory primordia, including the nascent sensory olfactory epithelium. However, the nasal placodes also function as signaling centers, crucial for the formation of the vertebrate nose, brain, and face. Variation in morphogenesis and patterning of the nasal placodes results in diverse phenotypic outcomes. In this study, the authors use enhanced-contrast CT to quantify the growth of the olfactory system and clarify how differences in morphogenetic timing partition the nasal cavity and associated olfactory system. The authors observe that axonal outgrowth from the olfactory epithelium, which eventually connects receptor neurons with the brain, begins earlier than previously thought. Furthermore, caudal olfactory projections into the telencephalon and diencephalon during embryogenesis play a role in neuronal tradeoffs impacting the size and morphology of the primary olfactory structures, including the olfactory turbinates (conchae), which are the bony protrusions in the nasal cavity.

“Analysis of Meis2 knockout mice reveals Sonic hedgehog-mediated patterning of the cochlear duct” by Hei Yeun Koo, Jae Hwan Oh, María Beatriz Durán Alonso, Iris López Hernández, Margarita González-Vallinas, María Teresa Alonso, Juan Tena, Alejandro Gil-Gálvez, Fernando Giraldez, Jinwoong Bok, and Thomas Schimmang. DevDyn 254.4, pp. 365–372. https://doi.org/10.1002/dvdy.747

The inner ear governs our sense of hearing and balance, and is composed of a bony and membranous labyrinth. The bony labyrinth is made up of the vestibule, semicircular canals, and cochlea, of which the cochlea plays a central role in hearing. The cochlea is a fluid-filled, spiral-shaped cavity that enables the transduction and perception of different frequencies of sound via sensory hair cells in the organ of Corti. The hair cells are arranged in a complex and precise mosaic pattern in rows; however, the mechanisms underlying the formation and patterning of the cochlea are still poorly understood. The authors previously noted that Meis2 loss-of-function in mice results in either a complete absence of the cochlea or abnormal cochlear outgrowth during inner ear development. In this study, the authors report that Meis2 mutant mice have ectopic and extra rows of sensory hair cells, a phenotype similar to that observed in Shh mutant mice. Thus, Meis-mediated Shh signaling is required for proper development of the cochlea.